Here are the specs for the external display connection of the Surface Pro 3 (SP3) from the Surface Pro 3 Wiki. Thanks, Robert

External display connectivity

The Surface Pro 3 is capable of connecting up to two external displays. Maximum supported resolutions varies across laplet configurations according to CPU model. The i3-model can drive up to two WUXGA (1920x1200 at 60 Hz) displays, while the i5 and i7 models support up to two external monitors with maximum resolution of 2880x1800 at 60 Hz. The maximum resolution of a single external display is 2560x1600 at 60 Hz for i3-based model and 3200x2000 at 60 Hz or 3840x2160 at 30 Hz (known as 4K Ultra HD) for i5 and i7-based models.[23]

So the SP3 does not support 3480x2160 60Hz, only at 30Hz. And the ASUS PB287Q does not support 3200x2000 resolutions or the 2560x1600 resolutions. So the max resolution you will be able to use with the SP3 and the PB287Q is 3480x2160 at 30 Hz.